Installation Issues: No Unity, Grub Rescue, Windows 10 Gone.

Hello,

I am installing Ubuntu on my home computer because I wish to do some scientific computing. Unfortunately, I have no experience with operating systems and I have run into many issues that I don't understand. After hours of googling, however, I leaed a little bit. Even still, I will need your help to solve these problems.

First, I want to tell you about the computer I have so that you can really understand everything.

Hardware
Intel Core i5-6500 3.2GHz Quad-Core Processor
Asus B150M-A D3 Micro ATX LGA1151 Motherboard
Crucial Ballistix Sport 16GB (2 x 8GB) DDR3-1600 Memory
EVGA GeForce GTX 960 4GB SuperSC ACX 2.0+ Video Card
Samsung 840 EVO 250GB 2.5" Solid State Drive
WD Blue 1TB SATA 6 Gb/s 7200 RPM 64MB Cache Hard Drive

Windows 10 was already installed on the Samung Solid-State Hard Drive (sda)
Now, I am attempting to install Ubuntu on the Hard Disk Drive (sdb) so that I can dual boot.

Now I will list some issues that seem most important to me.
1. I made a bootable USB using Rufus. I can launch Ubuntu from the bootable USB, however, I do not have any graphical interface. I can see a desktop and mouse. But there is no other graphical interface, I caot access the terminal using [Alt]+[Ctrl]+[T]. I did access the terminal using [Alt]+[Ctrl]+[F2]. Here, I was able to command "startx" so that files on the desktop appeared.
2. After installing Ubuntu, I caot boot from Windows 10. I can't load Windows 10 from either hard drive on the YUMI-BIOS screen.
3. If I boot from the solid-state hard drive (sda), I am led to a grub-rescue screen. If I boot from the hard disk drive, I am led to a grub screen.

What is the best way to go about solving these issues?

Dan